US3545420A

US3545420A - Capacitor discharge ignition system

Info

Publication number: US3545420A
Application number: US779563A
Authority: US
Inventors: Roland J Foreman; Arthur G Hufton
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1968-11-27
Filing date: 1968-11-27
Publication date: 1970-12-08
Anticipated expiration: 1987-12-08
Also published as: FR2024344A1; DE1958570A1; GB1283577A; DE1958570B2

Description

United States Patent [1113545320 [72] Inventors Roland J. Foreman References Cited Franklin Park; UNITED STATES PATENTS Arthur G. l-luiton, Elk Grove, Illinois 3,357,415 12/1967 Huntzinger... 123/143(E) [21] App]. No. 779,563 3,461,851 8/1969 Stephens 123/149 [22] Filed NOV. 27,1968 3,464.397 9/1969 Burson 123/148(E) [45] pauimed 1970 Primary Examiner-Laurence M. Goodridge [73] Assignee Motorola Inc. A" M n h l & R

Franklin Park, Illinois omeyue er, to e e auner a corporation of Illinois [54] CAPACITOR DISCHARGE IGNITIWSYSTEM 4 Claims, 2 Drawing Figs.

[52] US. Cl. 123/149,

123/148, 315/ ABSTRACT: A capacitor discharge ignition system for an iniii iiiifli'sazi;::::::::::::::::::::::::::::::::::::::::::"13383i? Wing is used both as a secondary winding for a step-up transformer and as a charge winding for charging the ignition capacitor.

PATENTEDnacsmm 3.5451420 INVENTOR ROLAND J. FOREMAN ARTHUR G. HUFTON BY AT TY S.

flam- CAPACITOR DISCHARGE IGNITION SYSTEM BACKGROUND OF THE INVENTION amount of space and have as little weight as possible. Therefore, electronic components are taking the place of mechani' cal apparatus formerly used in them. Furthermore, in order to be competitive in the marketplace the cost ofelectronic ignition systems must 1 compare favorably with the. cost of mechanical ignition systems. In most capacitor discharge ignition systems to date, wherein a flywheel is employed to generate a voltage in a coil for charging the ignition capacitor, separate coils are used for the charging winding and for the high voltage winding which provide the ignition pulses, thereby adding to thecost and size of the system.

SUMMARY. OF THE INVENTION it is an object of this invention to provide an improved capacitor discharge ignition system, for an internal com bustion engine, that is compact and inexpensive in comparison to previous capacitor discharge ignition systems. a i

It is another object of this invention to provide a capacitor discharge ignition system that compares favorably with mechanical ignition systems in reliability and cost.

In an embodiment of the invention a generator utilizes a magnet on theflywheel of an internal combustion engine to provide a relatively low amplitude alternating voltage pulse each time the magnet passes a charge winding. The repetition or occurrence rate of this alternating voltage is proportional to the angular velocity of the flywheel; and the polarity of portions of this alternating voltage is suitable to forward bias a solid state diode connected betweenthe charge winding and an ignition capacitor, to thereby charge the ignition capacitor. The generator charge winding is also connected to a spark gap. A silicon controlled rectifier (SCR) is triggered to discharge the ignition capacitor through a coupling coil which is inductively coupled to the generator charge winding. The voltage induced in the charge winding as a result of the discharge of the ignition capacitor is inverted in polarity and stepped up in amplitude to produce an arc across the spark gap. The inverted polarity of this high-tension ignition pulse reverse biases the solid state diode which isolates the ignition pulse from the ignition capacitor. The SCR can be triggered, for example, by a trigger signal obtained from a second generator winding placed in a spaced relation to the path of the magnet on the flywheel, or the trigger signal can be provided by a time base electrical network that includes a control capacitor connected between the ignition capacitor and the gate of the SCR. The decrease in impedance of the control capacitor with an increase in frequency of the charging voltage, due to increased flywheel r.p.m., causes the application of a trigger signal to the SCR whose instantaneous amplitude is proportional to the engine r.p.m. Therefore, an increase in en gine r.p.m. automatically results in a corresponding spark advance.

BRIEF DESCRIPTION OF THE DRAWINGS discharge ignition system in accordance with this invention;

and

FIG. 2 is another schematic diagramillustrating a second embodiment of the capacitor discharge ignition system of H6. 1. a

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawing, permanent magnet 11 is integral with the periphery of engine flywheel 13 which is rotated by the engine crankshaft both in a clockwise direction and in synchronism with the engine. Generator high voltage winding or charge winding 17 and trigger winding 19 are placed in a spaced relation to flywheel 13 adjacent to the circumferential path which permanent magnet 11 follows as the flywheel rotates. There is effectively no inductive coupling between

windings

17 and 19. When magnet llpasses charge winding 17 or trigger winding 19, magnetic flux from the magnet cuts across the turns of the winding and induces voltage pulses of alternating polarity therein. The amplitude of these pulses varies with the speed of magnet 11 which depends on the angular velocity of flywheel 13.

One end of charge winding 17 is connected both through the spark plug or gap 21 to a ground orireference potential and to the anode 23 of an electron control means or high voltage diode 24. Diode 24 has a high enough peak inverse voltage rating that it can withstand reverse voltages having amplitudes in excess of the amplitudes of ignition voltages used in ignition systems. One terminal of charge storage means or ignition capacitor 27 is connected to the cathodeZS of diode 24; the other terminal of capacitor 27 is connected to ground.

Anode 29 of controlled conductive means or SCR 31 is con nected to ignition capacitor 27. SCR gate 33is connected to one end of trigger winding 19, and cathode 35 is connected both to the other end of trigger winding 19 and to one end of primary or coupling winding37. The other end of winding 37 is connected to ground. Primary winding 37 is inductively couage of alternating polarity is applied between gate. 33 and cathode 35 of SCR 31. When SCR cathode 35 is positive with respect to gate 33 the SCR gate-cathode junction is reversed biased and the SCR is nonconductive. Diode 33 and current limiting resistor 40, connected between gate 33 and cathode 35, protect the gate-cathode junction of the SCR from this reverse biasing voltage. When the SSH cathode 35 is negative with respect to gate 33, the SCR gate-cathode junction tends to be forward biased; and the SCR is rendered conductive when the amplitude of this forward-biasing voltage exceeds the firing or threshold voltage for the SCR. When SCR 3]. conducts ignition capacitor 27 will discharge through SCR 31 and primary winding 37 to ground.

The voltage produced across winding 37 by the discharge of capacitor 2'7 will have the same polarity as the'voltage initially induced in high voltage winding 17 by magnet 11. Windings 3'7 and 17 will inductively change this relatively low voltage creased amplitude of the ignition voltage will be adequate to cause a high-tension spark across gap 21; and its inverted polarity will reverse bias diode 24 rendering it nonconductive thus isolating capacitor 27 from the ignition voltage. Hence, for each rotation of the flywheel an ignition spark is produced across spark gap 21. The spark repetition rate varies directly with the angular velocity or r.p.m. of flywheel 11 which depends on the r.p.m. of the engine.

While the charging voltage for ignition capacitor 27 is being induced in charge winding 17 by magnet 11, an alternating voltage of reduced amplitude is thereby inductively coupled into primary winding 37. Diode lit, which is connected across winding 37, suppresses voltages of the polarity to undesirably fire SCR 31 and increases the pulse width of the ignition pulse produced across gap 21. Semiconductor device M, which is connected across diode 42, can be rendered conductive by a voltage of either polarity provided that this voltage has a relatively high amplitude. The device is herein used to protect diode 42 from being damaged by excessive inverse voltages.

What has been described, therefore, is a relatively simple, compact and inexpensive capacitor discharge ignition system. It compares favorably in cost and reliability to mechanical ignition systems; and it uses a high voltage winding for the dual purposes of an ignition capacitor charge winding and a secondary winding of a high voltage step-up transformer thereby eliminating the expense, space requirement, and additional weight of the replaced winding.

FIG. 2 of the drawing illustrates another embodiment of the capacitor discharge ignition system which utilizes a time base electrical network connected from capacitor 27a to SCR gate 33a for providing spark advance proportional to the engine rpm. The serial arrangement of resistor 41 and potentiometer 43 is connected in parallel with ignition capacitor 27a. The potentiometer arm 45 is connected through coupling capacitor 47 to SCR gate 33a for providing trigger signals thereto.

The ignition capacitor 27a is charged by magnetically induced energy from high-voltage winding 17a. The instantaneous amplitude of the charge voltage across ignition capacitor 27a increases as magnet 11a approaches winding 17a. This charge voltage, of increasing amplitude, is applied to SCR gate 33a until the firing threshold is exceeded thus rendering SCR 31a conductive. Capacitor 270 then discharges through SCR 31a to subsequently produce an ignition pulse across the spark gap 21a.

The ignition pulse must occur an interval of time before the piston reaches TDC at the end of its compression stroke. The

length of the interval of time between the ignition pulse and TDC is the amount of spark advance. When the engine rpm. is increased the relative amount of time necessary for fuel combustion requires that the amount of spark advance be increased. When the rpm. increases the capacitive reactance of coupling capacitor 47 decreases because of the increased repetition rate of the charging voltage; therefore, adequate firing energy is applied through resistor 41, potentiometer 43 and capacitor 47 to gate 33a of the SCR earlier in the engines combustion cycle thus providing an amount of spark advance corresponding to the instantaneous engine r.p.m. The change in the amount of spark advance is, therefore, automatically determined by change in the engine speed. Furthermore, potentiometer 43 can be adjusted to vary the time constant of the time base circuit thereby adjusting the amount of spark advance according to difierent requirements.

Therefore, this second described embodiment provides the advantage of automatic and adjustable spark advance in addition to the cost, weight, and space saving features which were pointed out in reference to the first described embodiment of the capacitor discharge ignition system.

We claim:

. 1. In a capacitor discharge ignition system for an internal combustion engine, the combination including, electron control means, ignition capacitor means, flywheel means having magnetic means integral therewith; first coil means positioned at a spaced relation to said flywheel means, second coil means inductively coupled to said first coil means, means driving said flywheel means and said magnetic means in synchronism with the engine past said first coil means thereby cyclically generating a voltage therein, said electron control means coupling said generated voltage from said first coil means to charge said ignition capacitor, controlled conductive means, first circuit means connected to said controlled conductive means and providing a trigger signal thereto for selectively operating the same, second circuit means for said controlled conductive means connecting energy from said ignition capacitor to said second coil means upon the application of said trigger signal thereto, said second coil means being responsive to said energy to inductively couple a voltage to saidfirst coil means, said electron control means being responsive to said inductively cqtpled voltage to isolate said ignition capacitor therefrom, sai inductive y coupled voltage generating an ignition pulse in said first coil means and ignition means connected to receive said pulse for tiring the engine.

2. The discharge ignition system of claim 1 wherein said first circuit means providing a' trigger signal includes third coil means positioned in a spaced relation to said flywheel means.

3. The capacitor discharge ignition system of claim 1 wherein said first circuit means providing a trigger signal includes a resistive network in parallel with said ignition capacitor means, the system further including control capacitor means connected from said resistive network to said con trolled conductive device to apply trigger signals having an amplitude proportional to the repetition .rate of said cyclically generated voltage to said controlled conductive device.

4. The. capacitor discharge ignition system of claim 1 wherein said electron control means includes a solid state diode having a high inverse voltage rating.